Anterior cervical plate assembly

ABSTRACT

A cervical plate assembly is disclosed. The cervical plate assembly includes a base plate including: (1) at least two bone screw seats, each bone screw seat including a borehole dimensioned to receive a bone screw, and (2) a first blocking seat positioned between the at least two bone screw seats. The cervical plate assembly includes a blocking mechanism retained within the first blocking seat of the base plate. The blocking mechanism is selectively positionable between a closed position in which the blocking mechanism obstructs at least one bone screw seat to retain a bone screw with the base plate, and an open position in which the bone screw seats are unobstructed.

FIELD OF INVENTION

The present disclosure is related to a surgical implant, and is more particularly related to an anterior cervical plate.

BACKGROUND

Certain surgical procedures require a surgeon to fuse portions of a patient's spine to each other. Implanting a cervical plate reduces a patient's range of motion, and helps relieve pain experienced by a patient. Although cervical plate implantations are used to treat radiculopathy or myelopathy, but one of ordinary skill in the art would recognize that fusion can be used for other types of surgery.

Anterior cervical plate assemblies typically include a base plate defining through openings for bone screws to anchor the base plate to a patient's spine. Some cervical plate assemblies include a blocking mechanism to prevent the bone screws from inadvertently backing out of the base plate. One type of known blocking mechanism includes an automated blocking feature, such that once a bone screw passes a predetermined threshold then the blocking mechanism is automatically activated to block the bone screws from inadvertently backing out of the plate. These automated blocking mechanisms can be complicated for surgeons to operate, and can make removal of the base plate difficult.

Other known blocking mechanisms for anterior cervical plate assemblies rely on a patient's bones to have a certain strength characteristic to withstand the blocking mechanism features. Some known types of blocking mechanisms require force for removing a screw from the blocking mechanism. However, this type of blocking mechanism can cause stripping of the screw holes for bone screws implanted in a patient's bones.

Another known type of blocking mechanism for anterior cervical plate assemblies requires additional steps to install and lock the blocking mechanism screw in the plate. In some devices, this additional step requires a specialty tool or instrument. These steps are time consuming and require the surgeon to perform additional steps during surgery, which is undesirable.

It would be desirable to provide an improved cervical plate assembly that is relatively simple to use and provides a reliable blocking function.

SUMMARY

Briefly stated, an improved cervical plate assembly is disclosed. The cervical plate assembly includes a base plate including four bone screw seats. Each bone screw seat includes a borehole dimensioned to receive a bone screw. Each borehole defines a central axis that is (a) angled relative to a central lateral axis of the base plate at a first angle and (b) angled relative to a central longitudinal axis at a second angle. In one embodiment, the first angle is at least 25 degrees, and the second angle is at least 6 degrees. The base plate defines two retention slots that are each positioned between a pair of the four bone screw seats. The assembly includes two blocking mechanisms. Each blocking mechanism includes a biasing element arranged between a first blocking element and a second blocking element. The first blocking element is configured to obstruct a first bone screw seat of the four bone screw seats, and the second blocking element is configured to obstruct a second bone screw seat of the four bone screw seats. The first blocking element and the second blocking element are independently positionable from each other. Each blocking mechanism is retained within a respective one of the two retention slots. The blocking mechanisms are selectively positionable between a closed position in which the blocking mechanism obstructs at least one bone screw seat to retain a bone screw with the base plate, and an open position in which the bone screw seats are unobstructed.

A variety of arrangements and embodiments are described in more detail below and in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary as well as the following detailed description will be best understood when read in conjunction with the appended drawings. In the drawings:

FIG. 1 is a perspective view of one embodiment of a cervical plate assembly implanted on a patient's spine.

FIG. 2 is a perspective view of the cervical plate assembly of FIG. 1 including bone screws.

FIG. 3A is a perspective view of the cervical plate assembly of FIGS. 1 and 2 with a blocking mechanism in an open position.

FIG. 3B is a perspective view of the cervical plate assembly of FIGS. 1-3A with the blocking mechanism in a blocked position.

FIG. 4A is a top perspective view of the cervical plate assembly of FIGS. 1-3B including an installed bone screw with the blocking mechanism in the open position.

FIG. 4B is a top perspective view of the cervical plate assembly of FIGS. 1-4A including an installed bone screw with the blocking mechanism in the blocked position.

FIG. 5A is a top view of a cervical plate assembly according to one embodiment.

FIG. 5B is a side view of the cervical plate assembly of FIG. 5A.

FIG. 5C is a front view of the cervical plate assembly of FIGS. 5A and 5B.

FIG. 5D is a cross-sectional view along line 5D-5D of FIG. 5C.

FIG. 5E is a cross-sectional view along line 5E-5E of FIG. 5B.

FIG. 6A is a top view of a cervical plate assembly in an open position according to one embodiment.

FIG. 6B is a top view of the cervical plate assembly of FIG. 6A in a blocked position.

FIG. 6C is a side cross sectional view of the cervical plate assembly of FIGS. 6A and 6B including a bone screw in a blocked position.

FIG. 7A is a top view of a cervical plate assembly in an open position according to one embodiment.

FIG. 7B is a top view of the cervical plate assembly of FIG. 7A in a blocked position.

FIG. 7C is a perspective view of the cervical plate assembly of FIGS. 7A and 7B in the blocked position.

FIG. 7D is a cross section view of a blocking mechanism of the cervical plate assembly of FIGS. 7A-7C.

FIG. 8 is a perspective view of a cervical plate assembly in a blocked position according to one embodiment.

FIG. 9A is a top view of a blocking mechanism according to one embodiment.

FIG. 9B is a perspective view of the blocking mechanism of FIG. 9A.

FIGS. 9C-9E are perspective views of sub-components of the blocking mechanism of FIGS. 9A and 9B.

FIG. 10A is a top view of a cervical plate assembly including a bone screw in a blocked position according to one embodiment.

FIG. 10B is a perspective view of the cervical plate assembly of FIG. 10A.

FIG. 10C is a side cross section view of the base plate of FIGS. 10A and 10B.

FIG. 11A is a top view of an embodiment of a cervical plate assembly.

FIG. 11B is a side view of the cervical plate assembly of FIG. 11A.

FIG. 12 is a top view of an embodiment of a blocking mechanism.

FIG. 13 is a side view of an embodiment of a blocking mechanism associated with a bone screw.

FIG. 14A is a side view of a blocking mechanism according to one embodiment in an open position.

FIG. 14B is a side view of the blocking mechanism of FIG. 14A in a blocked position.

FIG. 14C is a top view of the blocking mechanism of FIGS. 14A and 14B.

FIG. 14D is a side view of a portion of the blocking mechanism of FIGS. 14A-14C.

FIG. 15A is a top view of a blocking mechanism according to one embodiment in a blocked position.

FIG. 15B is a top view of the blocking mechanism of FIG. 15A in an open position.

FIG. 16A is a top view of a blocking mechanism according to one embodiment.

FIG. 16B is a side cross section view of the blocking mechanism of FIG. 16A.

FIG. 17A is a magnified, side view a bone screw according to one embodiment.

FIG. 17B is a side view of the bone screw of FIG. 17A.

FIG. 17C is a cross section view of the bone screw of FIG. 17B along line 17C-17C.

FIG. 18A is a top view of a cervical plate assembly in a blocked position according to one embodiment.

FIG. 18B is a top view of the cervical plate assembly of FIG. 18A in an open position.

FIG. 18C is a side cross section view of a blocking mechanism for the cervical plate assembly of FIGS. 18A and 18B.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It is to be understood that the present disclosure is not limited in its application to the details of construction and the arrangement of components set forth in the description herein or illustrated in the drawings. The teachings of the present disclosure may be used and practiced in other embodiments and practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings.

The following discussion is presented to enable a person skilled in the art to make and use embodiments of the present disclosure. Various modifications to the illustrated embodiments will be readily apparent to those skilled in the art, and the principles herein can be applied to other embodiments and applications without departing from embodiments of the present disclosure. Thus, the embodiments are not intended to be limited to embodiments shown, but are to be given the widest scope consistent with the principles and features disclosed herein. The following detailed description is to be read with reference to the figures, in which like elements in different figures have like reference numerals. The figures, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of the embodiments. Skilled artisans will recognize the examples provided herein have many useful alternatives and fall within the scope of the embodiments.

FIG. 1 illustrates a cervical region of a patient's spine 1 with an anterior cervical plate assembly 10 implanted on the spine 1. As shown in FIG. 1, the plate assembly 10 is implanted at the C4-C5 vertebrae of the spine 1. One of ordinary skill in the art would recognize that the plate assembly 10 could be installed at different regions of the patient's spine 1. The term plate assembly is generically used herein to generally refer to the plate assemblies described in some of the embodiments. In one embodiment, the plate assemblies are specifically designed to be used for anterior cervical implantations. One of ordinary skill in the art would understand from the present disclosure that the concepts and features of the plate assemblies disclosed herein could be adapted for surgical assemblies and techniques for other portions of a user's anatomy besides the spine. With respect to FIG. 1, the anterior cervical plate assembly 10 is shown including four bone screws 12 a-12 d and two blocking assemblies 14 a, 14 b, however one of ordinary skill in the art would recognize from the present disclosure that alternative arrangements of the anterior cervical plate assembly 10 could be used. For instance, the cervical plate assembly can extend to multiple levels of the spine and include additional screw holes for additional fixation to adjacent vertebral bodies. The bone screws used in any of the embodiments described herein can be self-drilling, self-tapping, variable angle, fixed angle, or any other known type of bone screw design. Additionally, the embodiments of the base plate described herein can be configured to accept bone screws having screw diameters of 4.2 mm and 4.6 mm, although one of ordinary skill in the art would understand that different sizes for bone screws can be used. FIG. 2 illustrates the plate assembly 10 with the bone screws 12 a-12 d and the blocking mechanisms 14 a, 14 b in an uninstalled state. As shown in FIG. 2, the plate assembly 10 includes two pairs of bone screws 12 a-12 d, with each pair configured to be implanted into a vertebral body. In this embodiment, the blocking mechanisms 14 a, 14 b each include a blocking screw 15 a, 15 b. The blocking screws 15 a, 15 b each include a head 16 a, 16 b with a varying circumferential edge 17 a, 17 b, and an engagement recess 20 a, 20 b configured to be engaged by a tool for rotationally driving the heads 16 a, 16 b. One of ordinary skill in the art would understand from the present disclosure that the geometry of the engagement recesses 20 a, 20 b can be varied. In one embodiment, the engagement recess can be omitted and the blocking mechanisms 14 a, 14 b can be manually engaged/actuated by a user.

As shown in FIG. 2, the circumferential edges 17 a, 17 b of the blocking screws 15 a, 15 b include diametrically opposed cutouts 18 a, 18 b, and diametrically opposed lobes 19 a, 19 b. The cutouts 18 a, 18 b are dimensioned to allow passage of the bone screws 12 a-12 d when the cutouts 18 a, 18 b overlap an associated bone screw seat. The lobes 19 a, 19 b are configured to obstruct an associated bone screw seat to block the bone screws 12 a-12 d from backing out of the plate assembly 10. The engagement recesses 20 a, 20 b are illustrated with a hexagonal profile, but one of ordinary skill in the art would recognize from the present disclosure that any non-round profile can be used. The heads 16 a, 16 b are engaged by a user and rotated a quarter turn, i.e. 90 degrees, to move from a blocked position, in which bone screws 12 a-12 d are retained with the plate assembly, to an open position, in which the bone screws 12 a-12 d can be removed from the plate assembly 10. As used herein, the blocked position corresponds to a position in which the bone screws seats are obstructed and the open position corresponds to a position in which the bone screw seats are unobstructed.

FIG. 3A illustrates an open configuration for the blocking mechanisms 14 a, 14 b, and FIG. 3B illustrates a blocked configuration for the blocking mechanisms 14 a, 14 b. As shown in FIGS. 3A and 3B, the plate assembly 10 includes a base plate 11 that defines bone screw seats 22 a-22 d for a respective one of the bone screws 12 a-12 d. The plate 11 also defines blocking mechanism seats 24 a, 24 b, shown in FIG. 3B, which are configured to retain a respective one of the blocking mechanisms 14 a, 14 b. As illustrated in this embodiment, the blocking mechanism seats 24 a, 24 b include a retention lip 25 a, 25 b that prevents the blocking mechanisms 14 a, 14 b from being removed from the plate 11. One of ordinary skill in the art would recognize from the present disclosure that alternative retention arrangements could be provided for ensuring the blocking mechanisms 14 a, 14 b are retained with the plate 11. For example, the blocking mechanisms 14 a, 14 b could be retained with the plate 11 by tabs, prongs, elastic elements, slots, channels, or other retention features. In one embodiment, the blocking mechanisms 14 a, 14 b can include an enlarged head on an opposite end from the screw heads 16 a, 16 b and the plate 11 can define a retention recess dimensioned to captively secure the enlarged head of the blocking mechanisms 14 a, 14 b. One of ordinary skill in the art would recognize from the present disclosure that a variety of retention features could be used, as long as the retention features retain the blocking mechanisms 14 a, 14 b with the base plate 11 while also allowing the blocking mechanisms 14 a, 14 b to rotate.

FIGS. 4A and 4B illustrate the plate assembly 10 including a single bone screw 12 b. FIG. 4A illustrates the blocking mechanism 14 a in an open position in which the bone screw 12 b can be removed from the base plate 11. FIG. 4B illustrates the blocking mechanism 14 b in a blocking position in which the bone screw 12 b is blocked from backing out of the plate assembly 10.

FIGS. 5A-5E illustrate a base plate 211, and specifically illustrate the relatively high angulation of the bone screw seats 222 a-222 d. The base plate 211 includes a central window 209, which can be used by a surgeon during installation to view the disc space (and interbody implant). This window 209 can be used to assist in making sure the base plate 211 is the correct position. Although the window 209 is only illustrated in the embodiment of FIGS. 5A-5E, one of ordinary skill in the art would recognize from the present disclosure that the window 209 can be integrated into the design of any of the base plates disclosed herein. The plate 211 includes two blocking mechanisms 214 a, 214 b. As shown in FIG. 5A, the plate 211 defines channels 207 a, 207 b for each of the blocking mechanisms 214 a, 214 b in which blocking elements can slide. Blocking elements (not shown in FIG. 5A) are retained within the channels 207 a, 207 b and are driven outward to the bone screw seats 222 a-222 d to retain bone screws with the plate 211. A tapered profile defined by the channels 207 a, 207 b is shown in FIG. 5D. The blocking elements of the blocking mechanism 214 a, 214 b have a complementary profile such that the blocking elements are retained in the channels 207 a, 207 b and can slide within the channels 207 a, 207 b. The channels 207 a, 207 b define a laterally outer stop surface for the blocking elements.

As shown in FIG. 5A, the base plate 211 is divided by two primary axes: a central lateral axis X₁ and a central longitudinal axis X₂. The high angulation of the bone screw seats 222 a-222 d provides a strong and rigid construction for attaching bone screws to a patient. The plate 211 allows bone screws to be inserted at high cephalad and caudal angles. The high angulation also allows for longer bone screws to be used for implantation, which corresponds to increased mechanical purchase and improved strength of the implantation. Each of the bone screw seats 222 a-222 d define a borehole 223 a-223 d with a central axis CA₁-CA₄. Each central axis CA₁-CA₄ of boreholes 223 a-223 d is angled relative to the central lateral axis X₁ of the base plate 211 at a first angle θ₁. In one embodiment, the first angle θ₁ is between 50-75 degrees. In one embodiment, the first angle θ₁ is at least 65 degrees. In one embodiment, the first angle θ₁ is at least 70 degrees. Each central axis CA₁-CA₄ of boreholes 223 a-223 d is also angled relative to the central longitudinal axis X₂ at a second angle θ₂. In one embodiment, the second angle θ₂ is between 4-8 degrees. In one embodiment, the second angle θ₂ is at least 6 degrees. Both the first angle θ₁ and the second angle θ₂ can be varied depending on the type of bone screw being used in a particular assembly. During installation, the threaded ends of bone screws inserted into bone screw seats 223 a and 223 b (with respect to the view shown in FIG. 5A) are angled or canted towards each other on an underside of the base plate 211 due to the second angle θ₂. Although the angulation of the central axes CA₁-CA₄ of the boreholes 223 a-223 d for the bone screw seats 222 a-222 d are only specifically illustrated in FIGS. 5A-5E and explained with respect to these figures, one of ordinary skill in the art would understand that these angulation values are present for any of the other embodiments of the base plate described herein.

FIGS. 6A-6C illustrate another embodiment of a plate assembly 310 including a base plate 311. As shown in FIGS. 6A-6C the plate assembly 310 includes two bone screw seats 322, with a single bone screw 312 arranged in one of the bone screw seats 322. This plate assembly 310 is only illustrated with two bone screw seats 322, but one of ordinary skill in the art would understand that the features of this embodiment can be adapted for a plate assembly including any number of bone screw seats. This plate assembly 310 is also illustrated as having a generic rectangular profile, however one of ordinary skill in the art would understand that the profile of the plate itself can vary, and can resemble the profile of the base plate 11 described above.

The plate assembly 310 includes a blocking mechanism 314 having a different profile than the blocking mechanisms 14 a, 14 b of FIGS. 1-3B. The blocking mechanism 314 includes a head 316 with a varying circumferential edge 317, and an engagement recess 320 configured to engage a tool for rotationally driving the blocking mechanism 314. The edge 317 includes diametrically opposed cutouts 318, and diametrically opposed lobes 319. The cutouts 318 are dimensioned to allow insertion of the bone screw 312, and the lobes 319 are configured to block the bone screw 312 from backing out of the plate assembly 310. The lobes 319 are also configured to deflect inward when the bone screw is inserted and then blocks the bone screw from backing out. The circumferential edge 317 of the blocking mechanism 314 has a symmetrical profile such that the blocking mechanism 314 provides an identical profile if the blocking mechanism 314 is rotated 180°. Slots 321 are provided on the blocking mechanism 314 which provide grips or insertion points for a tool for rotating the blocking mechanism 314. FIG. 6A illustrates the blocking mechanism 314 in an open position, and FIG. 6B illustrates the blocking mechanism 314 in a blocked position without a bone screw 312. FIG. 6C illustrates a side cross section view of the plate assembly 310. As shown in FIG. 6C, the plate 311 defines a blocking mechanism seat 324 which axially retains the blocking mechanism 314 within the plate 311. The plate 311 defines grooves 313 configured to engage a threading 323 defined on the blocking mechanism 314. It should be noted that, a bone screw can be inserted into screw holes even when the blocking mechanism 314 is in a blocked position as shown in FIG. 6B, as the lobes of the blocking mechanism may be deformable. As shown in FIG. 6C, a clearance (c) is defined between the blocking mechanism 314 and the bone screw 312 when the bone screw 312 is fully seated in the bone screw seat 322. Although the clearance (c) is only illustrated with respect to this embodiment, one of ordinary skill in the art would recognize that the clearance can be provided in any of the other embodiments described herein.

FIGS. 7A-7D illustrate another embodiment of a plate assembly 410 and a base plate 411. The blocking mechanism 414 includes a head 416 having a generally X-shaped profile, and including four arms 428. Resilient blocking elements 426 extend between a respective pair of the four arms 428 on diametrically opposed sides of the head 416. Reliefs 427 are provided on sides of the head 416 including the resilient blocking elements 426. These reliefs 427 allow for the resilient blocking elements 426 to deform radially inwardly towards a central rotational axis of the blocking mechanism 414. FIG. 7A illustrates the blocking mechanism 414 in an open position. FIG. 7B illustrates the blocking mechanism 414 is a blocked position, with the resilient blocking elements 426 overlapping the bone screw seats 422. This particular blocking mechanism 414 can be in either the open or blocked position and still allow insertion of the bone screw 412 into the plate assembly 410. This embodiment allows for the bone screw 412 to be inserted into the plate assembly 410 when the blocking mechanism 414 is in the blocked position (FIG. 7B) due to elastic deformation of the resilient blocking elements 426 during insertion of the bone screw 412. Once fully inserted and installed, the bone screw 412 is prevented from backing out of the plate assembly 410 due to the resilient blocking elements 426. In one embodiment, the resilient blocking element 426 is formed from spring steel. In another embodiment, the resilient blocking element 426 is formed from an elastomeric material. One of ordinary skill in the art would recognize from the present disclosure that alternative types of blocking elements 426 can be used as long as the blocking elements 426 are configured to elastically deform during insertion of the bone screws and return to an initial position after insertion that blocks or overlaps with the inserted bone screw. FIG. 7C illustrates the plate assembly 410 in a perspective view with the blocking mechanism 414 in a blocked position. As shown more clearly in FIG. 7D, the blocking mechanism 414 includes cutouts 418 that are dimensioned to allow passage of the bone screws 412.

FIG. 8 illustrates another embodiment of a plate assembly 510 in a blocked position. The plate assembly 510 includes a blocking mechanism 514 including blocking lobes 519. The blocking lobes 519 may have a rectangular profile. One of ordinary skill in the art would recognize from the present disclosure that the profile of the lobes can be modified.

FIGS. 9A-9E illustrate another embodiment of a blocking mechanism 614. The blocking mechanism 614 of FIGS. 9A-9E can be integrated into any of the plate assemblies described herein. The blocking mechanism 614 includes a hub 650, a blocking element 654, and retention washer 658. The hub 650 defines grooves for accommodating the blocking element 654. The blocking element 654 defines lobes on diametrically opposite sides of the blocking element 654, each configured to block a bone screw within a cervical plate assembly. The blocking element 654 can be formed as a wire forming a continuous loop. The blocking element 654 can be snapped into or placed into the grooves formed on the hub 650, and a retention washer 658 can then be pressed or snapped onto a bottom end of the hub 650. The retention washer 658 can be snapped into a groove formed on the hub 650 such that the blocking element 654 is retained between the hub 650 and the retention washer 658. The blocking mechanism 614 can be rotated while retained within a seat of a base plate, such that the blocking element 654 moves from a position overlapping with a bone screw seat to block the bone screw seat, to an open position in which the blocking element 654 is rotated away from the bone screw seat and the bone screw seat is unobstructed.

FIGS. 10A-10C illustrate another embodiment of a plate assembly 710. The plate assembly 710 includes a blocking mechanism 714 including blocking tabs 719 arranged on opposite sides of a central portion 729. The blocking tabs 719 are configured to provide obstructions to an underlying bone screw seat, such that a bone screw is retained with the plate assembly 710. The central portion 729 includes resilient arms 731, such that the blocking mechanism 714 can be deformed by applying inward pressure to the blocking tabs 719. The resilient arms 731 form an X-shaped configuration with reliefs 733 formed between the arms 731. A user can manually pinch the blocking tabs 719 towards each other, and the blocking mechanism 714 can be manipulated from an open position to a blocked position without the use of a tool. The blocking mechanism 714 can be retained with the base plate 711 via a slot 721 formed in the base plate 711, or other retention configuration. As shown in FIG. 10C, the slot 721 has a tapered profile, and the blocking mechanism 714 has a complementary tapered profile such that the blocking mechanism 714 is retained within the slot 721. One of ordinary skill in the art would understand from the present disclosure that this slot 721 can be integrated into any of the base plates described herein to retain a blocking mechanism.

FIGS. 11A and 11B illustrate another embodiment of a plate assembly 810 including a blocking mechanism 814. The blocking mechanism 814 includes a central hub 816 defining a pair of C-shaped arms 816 a, 816 b, with resilient blocking elements 826 extending therebetween. Blocking tabs 819 are engaged against a respective one of the resilient blocking elements 826. Reliefs 827 are formed on the hub 816, and the reliefs 827 are dimensioned to each accommodate one of the resilient blocking elements 826 and one of the blocking tabs 819. FIG. 11A illustrates the blocking mechanism 814 in an expanded state in which the blocking tabs 819 are extended and configured to block a bone screw seat. The blocking mechanism 814 is configured to be rotated by 90° such that the blocking tabs 819 and the resilient blocking elements 826 are pushed inwardly into a respective one of the reliefs 827, and the blocking tabs 819 and the resilient blocking elements 826 are in a compressed state. The blocking tabs 819 can be retained within slots formed in the base plate 811, such that the blocking tabs 819 slide within the slots.

FIG. 12 illustrates an alternative configuration for a blocking mechanism 914 in which two blocking screws 914 a, 914 b are provided for blocking a respective bone screw seat. As shown in FIG. 12, a single blocking screw 914 a includes an engagement recess 920 configured to be engaged by a tool to rotate the blocking screw 914 a. Each of the blocking screws 914 a, 914 b include teeth 937 a, 937 b which engage each other such that rotation of the first blocking screw 914 a drives rotation of the second blocking screw 914 b. The blocking screws 914 a 914 b each define a blocking lobe 919 a, 919 b and a cutout 918 a, 918 b such that in a blocked position the blocking lobes 919 a, 919 b overlap with a bone screw seat, and in an open position the cutouts 918 a, 918 b overlap with a bone screw seat to allow for insertion of a bone screw.

FIG. 13 illustrates a blocking mechanism 1014 that is directly integrated with a bone screw 1012. As shown in FIG. 13, the bone screw 1012 is inserted into a base plate 1010, and the blocking mechanism 1014 provides axial retention of the bone screw 1012 relative to the base plate 1010. The blocking mechanism 1014 is formed as a split ring element, which is retained within a groove 1013 formed in a head of the bone screw 1012. A tool including a sleeve can be inserted around the head of the bone screw 1012 to push the blocking mechanism 1014 into the groove 1013 of the bone screw 1012. The blocking mechanism 1014 can define a tapered edge 1014′ which is configured to engage against the base plate 1010 during insertion, such that the tapered edge 1014′ slides along the base plate 1010 and the blocking mechanism 1014 is pushed into the groove 1013.

FIGS. 14A-14D illustrate a blocking mechanism 1114 including two blocking elements 1114 a, 1114 b, a central resilient element 1126, and two blocking resilient elements 1126 a, 1126 b. As shown in FIG. 14A, the blocking resilient elements 1126 a, 1126 b are engaged against a base plate 1111, and retain the blocking elements 1114 a, 1114 b in a first position, which can correspond to an open configuration. The central resilient element 1126 biases the blocking elements 1114 a, 1114 b outward from each other, but the blocking resilient elements 1126 a, 1126 b define a stop against the base plate 1111 and prevent this outward movement in FIG. 14A. As shown in FIG. 14B, once the blocking resilient elements 1126 a, 1126 b are downwardly depressed, then the central resilient element 1126 drives the blocking elements 1114 a, 1114 b outward to a second position, which can correspond to a blocked position. FIG. 14C shows a top view of the blocking mechanism 1114 with the blocking elements 1114 a, 1114 b in the blocked position and overlapping the bone screw seats 1122 a, 1122 b. FIG. 14D illustrates the blocking mechanism 1114 separate from the base plate 1111. In one embodiment, the blocking resilient elements 1126 a, 1126 b are pressed downward via a tool. One of ordinary skill in the art would recognize that the blocking resilient elements 1126 a, 1126 b can be pressed downward by a user/surgeon. In one embodiment, the blocking resilient elements 1126 a, 1126 b are leaf springs, but one of ordinary skill in the art would recognize from the present disclosure that alternative blocking elements can be used.

FIGS. 15A and 15B illustrate another embodiment of a blocking mechanism 1214. In this embodiment, the blocking mechanism 1214 includes a central blocking element 1219 that moves between a blocked position shown in FIG. 15A and an open position in FIG. 15B in which the bone screw seats 1222 a, 1222 b are either obstructed (FIG. 15A) or unobstructed (FIG. 15B). The central blocking element 1219 is a flexible plate that extends between lateral sides of the base plate 1211. A blocking cam 1226 is arranged within a slot 1221 formed on the base plate 1211. The blocking cam 1226 is configured to be positioned in a lower position within the slot 1221, as shown in FIG. 15A, in which the central blocking element 1219 is flexed to overlap with the bone screw seats 1222 a, 1222 b. The terminal ends of the central blocking element 1219 are understood to be fixed to the lateral sides of the base plate 1211 such that the central blocking element 1219 flexes and exhibits inflexion as shown in FIG. 15A. As shown in FIG. 15B, as the blocking cam 1226 is moved upward within the recess 1221, then the central blocking element 1219 returns to a relatively straight profile such that the central blocking element 1219 does not overlap with the bone screw seats 1222 a, 1222 b.

FIGS. 16A and 16B illustrate an alternative embodiment of a bone screw 1312 including a screw head 1315. The screw head 1315 includes a slot 1316 and a relief 1317. The relief 1317 is centered relative to a shaft of the bone screw 1312. The relief 1317 acts as a drive feature to help thread the screw 1312 and allows the screw head 1315 to compress to reduce the outer diameter of the screw head 1315. By having a nominal screw head diameter larger than a bone screw hole diameter defined on the base plate, the screw head 1315 provides an interference fit with the base plate when the driver tool is not engaged. When the bone screw 1312 is fully seated within an associated base plate, and the driver tool is removed from the screw head 1315, then the screw head 1315 expands back open to its nominal diameter, which is oversized relative to the associated bone screw seat and prevents the bone screw 1312 from backing out of the plate. Although an interference type fit is described with respect to this embodiment, one of ordinary skill in the art would recognize from the present disclosure that alternative arrangements could be provided to ensure that the bone screw 1312 has a secure connection to the base plate after insertion. Additionally, although a slot/relief arrangement is described with respect to this embodiment, one of ordinary skill in the art would recognize from this disclosure that alternative geometries can be used to achieve the same result of fixing the bone screw relative to a bone screw seat defined by a base plate.

FIGS. 17A-17C illustrate an alternative embodiment of a bone screw 1412. As shown in FIG. 17A, the bone screw 1412 has a screw head 1415 with a relief 1415′. The relief 1415′ is configured to accommodate a portion of a blocking mechanism 1414 (shown in dashed lines in FIG. 17A). This relief 1415′ allows for the blocking mechanism to partially overlap an axial end of the bone screw 1412, and as a result allows for a thinner base plate. The relief 1415′ also ensures that the blocking mechanism sufficiently overlaps with the bone screw 1412 in the axial direction.

FIGS. 18A-18C illustrate another embodiment of a blocking mechanism 1514. The blocking mechanism 1514 includes a central biasing element 1526 and two blocking elements 1526 a, 1526 b on opposite ends of the central biasing element 1526. The blocking mechanism 1514 is retained to a base plate 1511, and the base plate 1511 includes bone screw seats 1522 a, 1522 b (a single bone screw 1512 is shown within the base plate 1511). As shown in FIG. 18A, the blocking elements 1526 a, 1526 b are in the extended position due to the biasing force from the biasing element 1526. In this position, the blocking elements 1526 a, 1526 b overlap with the bone screw seats 1522 a, 1522 b and are in a blocked position to retain the bone screws with the base plate 1511. In FIG. 18B, the blocking elements 1526 a, 1526 b are in a compressed configuration with the biasing element 1526 being compressed and housed within cavities of the blocking elements 1526 a, 1526 b. In this configuration, the blocking elements 1526 a, 1526 b are positioned away from the bone screw seats 1522 a 1522 b such that the bone screw 1512 can be removed from the base plate 1511. The blocking elements 1526 a, 1526 b can be independently moved with respect to each other such that a bone screw 1512 can be removed from one of the bone screw seats 1522 a, 1522 b while a bone screw 1512 is blocked in the other one of the bone screw seats 1522 a, 1522 b. The central biasing element 1526 can be a coil spring, leaf spring, or any other type of elastic component. As shown in FIG. 18C, the blocking elements 1526 a, 1526 b are retained in the base plate 1511 via a mating slot feature. As shown in FIG. 15C, the base plate 1511 defines a slot 1517 with a protrusion 1517′ and the blocking element 1526 a includes a groove 1526 a′. One of ordinary skill in the art would recognize from the present disclosure that alternative types of retention/mating features can be used to slidingly retain the blocking elements 1526 a, 1526 b with the base plate 1511. For example, the retention can be achieved via a t-slot, dovetail, or other mating feature. The blocking elements 1526 a, 1526 b are slidingly retained within the slot 1517. In one embodiment, a cover can be integrated into the base plate 1511 that covers the central biasing element 1526 to protect the central biasing element 1526. As shown in FIG. 18C, the blocking elements 1526 a, 1526 b define a housing cavity 1527 which is dimensioned to house a portion of the central biasing element 1526. As shown in FIG. 18C, the blocking mechanism 1514 is completely retained within the slot 1517 such that the blocking mechanism 1514 does not extend above an upper surface 1511 a defined by the base plate 1511. This arrangement provides a lower profile for the plate assembly since the blocking mechanism 1514 does not add any additional height to the plate assembly.

Although several embodiments have been disclosed in the foregoing specification, it is understood that many modifications and other embodiments will come to mind, having the benefit of the teaching presented in the foregoing description and associated drawings. It is thus understood that the scope of the embodiments described herein are not limited to the specific embodiments disclosed hereinabove, and that many modifications and other embodiments are intended to be included within the scope of the appended claims.

It is further envisioned that features from one embodiment may be combined or used with the features from a different embodiment described herein. Moreover, although specific terms are employed herein, as well as in the claims which follow, they are used only in a generic and descriptive sense, and not for the purposes of limiting the described embodiments, nor the claims which follow. 

What is claimed is:
 1. A plate assembly comprising: a base plate including: at least two bone screw seats, each bone screw seat including a borehole dimensioned to receive a bone screw, and a first blocking seat positioned between the at least two bone screw seats; and a blocking mechanism retained within the first blocking seat of the base plate, the blocking mechanism being selectively positionable between a closed position in which the blocking mechanism obstructs at least one bone screw seat of to retain a bone screw with the base plate, and an open position in which the bone screw seats are unobstructed.
 2. The plate assembly of claim 1, wherein each borehole defines a central axis (a) angled relative to a central lateral axis of the base plate at a first angle, and (b) angled relative to a central longitudinal axis at a second angle.
 3. The plate assembly of claim 2, wherein the first angle is at least 25 degrees.
 4. The plate assembly of claim 2, wherein the second angle is at least 6 degrees.
 5. The plate assembly of claim 1, wherein the place assembly includes at least four bone screw seats.
 6. The plate assembly of claim 1, wherein the blocking mechanism includes a biasing element arranged between a first blocking element and a second blocking element, wherein the first blocking element is configured to obstruct a first bone screw seat of the at least two bone screw seats, and the second blocking element is configured to obstruct a second bone screw seat of the at least two bone screw seats, and the first blocking element and the second blocking element are independently positionable from each other.
 7. The plate assembly of claim 6, wherein the blocking mechanism is retained within the first blocking seat via a tapered slot formed in the base plate.
 8. The plate assembly of claim 1, wherein the blocking mechanism includes a screw head defining a circumferential edge having diametrically opposed cutouts, wherein the diametrically opposed cutouts are dimensioned for insertion and removal of a bone screw.
 9. The plate assembly of claim 8, wherein the screw head includes an engagement recess configured to be engaged by a tool for rotating the blocking mechanism within the first blocking seat.
 10. The plate assembly of claim 8, wherein the screw head is rotated by 90 degrees to move from the closed position to the open position.
 11. The plate assembly of claim 1, wherein the blocking mechanism includes a screw head including two pairs of arms diametrically opposed from each other, and two resilient blocking elements each extending between a respective pair of the two pairs of arms.
 12. An anterior cervical plate assembly comprising: a base plate including: four bone screw seats, each bone screw seat including a borehole dimensioned to receive a bone screw, each borehole defining a central axis that is (a) angled relative to a central lateral axis of the base plate at a first angle and (b) angled relative to a central longitudinal axis at a second angle, wherein the first angle is at least 25 degrees, and the second angle is at least 6 degrees; and two retention slots, each retention slot being positioned between a pair of the four bone screw seats; and two blocking mechanisms, each blocking mechanism including a biasing element arranged between a first blocking element and a second blocking element, wherein the first blocking element is configured to obstruct a first bone screw seat of the four bone screw seats, and the second blocking element is configured to obstruct a second bone screw seat of the four bone screw seats, and the first blocking element and the second blocking element are independently positionable from each other; each blocking mechanism is retained within a respective one of the two retention slots, the blocking mechanisms are selectively positionable between a closed position in which the blocking mechanism obstructs at least one bone screw seat to retain a bone screw with the base plate, and an open position in which the bone screw seats are unobstructed.
 13. The anterior cervical plate assembly of claim 12, wherein the two retention slots each define a first profile having tapered side walls, and the blocking elements of the blocking mechanisms each define a second profile that is complementary to the first profile.
 14. The anterior cervical plate assembly of claim 12, further comprising bone screws configured to be inserted within a respective one of the bone screw seats, wherein the bone screws each include a screw head defining a relief groove, and each relief groove is dimensioned to receive a portion of a respective one of the blocking mechanisms.
 15. The anterior cervical plate assembly of claim 12, wherein the base plate defines a through window, and the through window is positioned between the two retention slots.
 16. The anterior cervical plate assembly of claim 12, wherein the first blocking element and the second blocking element each define a housing cavity dimensioned to receive a portion of the biasing element.
 17. A plate assembly comprising: a base plate including: four bone screw seats, each bone screw seat including a borehole dimensioned to receive a bone screw, each borehole defining a central axis that is (a) angled relative to a central lateral axis of the base plate at a first angle and (b) angled relative to a central longitudinal axis at a second angle; and two retention slots, each retention slot being positioned between a pair of the four bone screw seats; and two blocking mechanisms, each blocking mechanism is retained within a respective one of the two retentions lots, and each blocking mechanism includes a biasing element arranged between a first blocking element and a second blocking element such that the first blocking element and the second blocking element are independently positionable from each other, wherein (a) when the biasing element is in an expanded state then the first blocking element obstructs a first bone screw seat of the four bone screw seats, and the second blocking element obstructs a second bone screw seat of the four bone screw seats, and (b) when the biasing element is in a compressed state then the first blocking element and the second blocking element are positioned away from the bone screw seats and the bone screw seats are unobstructed.
 18. The plate assembly of claim 17, wherein the biasing element is a coil spring.
 19. The plate assembly of claim 17, wherein each blocking mechanism is completely retained within a respective one of the two retention slots slot such that each blocking mechanism is positioned below an upper surface of the base plate.
 20. The plate assembly of claim 17, wherein the first angle is at least 25 degrees, and the second angle is at least 6 degrees. 